(The online version of this article appears in two parts. Click here to go to part one.)

THE real trouble started as early as 1957, when Gell-Mann returned from a wilderness trek in northern California to find Feynman strutting around the department proclaiming an epiphany: in a moment of intense clarity he had seen the very secret of what is known as the weak nuclear force, the engine of radioactive decay. Gell-Mann was dumbfounded. He had been mulling over the problem for weeks, and had come to a similar conclusion. But, typically, he hadn't written the idea up.

Ever since he was in college, Gell-Mann had suffered from a debilitating case of writer's block. He had failed to complete his senior thesis at Yale and had struggled over his Ph.D. dissertation on nuclear theory, preferring to hole up in the library reading the Tibetan Book of the Dead. Now fearful of being scooped, he rushed to beat Feynman into print. Finally the department chairman intervened, persuading his two stars that it would look silly to have competing papers come from the same campus. They agreed to collaborate.

When the theory made its debut, in January of 1958, it lacked the Gell-Mann touch: bereft of a clever name, it was dully called the V-minus-A model. But the power of the idea showed through. Always looking for the scientist who would become heir apparent to "the mantle of Einstein," the news media seized on the two geniuses from Caltech. Newsweek declared that the "dapper, cocky" Gell-Mann was many physicists' choice for "brightest light in his esoteric field." With a "Madison Avenue fastidiousness about his clothes" and his "boyish face and quick tongue," the magazine observed, Gell-Mann exhibited "a kind of sharp intellectual fussiness that has more than once wounded his colleagues." Time weighed in with a portrait of Feynman as a bongo-playing beatnik of uncanny mathematical powers who liked to pick locks in his spare time. Explaining a recent decision to become a teetotaler, Feynman said, "I got potted in a Buffalo bar one night and wound up with a lulu of a black eye."

Unaware of how forced the partnership had been, some physicists thought they saw the beginning of a powerful intellectual alliance, with the world's two smartest physicists taking on science's remaining mysteries. Gell-Mann seemed to have the same hope. Though Feynman was essentially a loner, Gell-Mann loved the camaraderie of collaboration. And he was terrified of heading solo into the void with an idea that might turn out to be wrong. He and Feynman had been trying to understand a problem involving neutrinos, the evanescent particles that fly through planets almost as easily as through empty space. The puzzle could be explained, they surmised, if there were actually two kinds of neutrinos (they called them red and blue). Gell-Mann wanted to write up the idea, but when Feynman resisted, he didn't have the nerve to go it alone. The theory, with others' names on it, later turned out to be correct, and Gell-Mann added Feynman's obstinacy to his lengthening list of grievances.

GELL-MANN spent 1959 working in Paris, polishing his French and indulging a growing taste for haute cuisine. After long, wine-soaked lunches with his French colleagues he would return, a little bleary, to his office at the Collège de France and ponder his next big problem: How were the dozens of different particles that kept popping up in accelerator experiments related? Appearing in many shapes and sizes, they appeared to have been created almost at random -- an affront to the search for order.

In December of 1960, after a chance conversation with a Caltech mathematician, Gell-Mann saw how to make the particles fit together beautifully in groups of eight. The Israeli physicist Yuval Ne'eman came up with the same idea at the same time, calling it by its mathematical name, SU(3). Gell-Mann, as usual, picked the name that endured: because he had been reading about Buddhism, he decided to call his classification scheme the Eightfold Way, a mocking reference to the Buddha's eight-step plan for righteous living. Ne'eman later said that one of the crucial things he learned from Gell-Mann was the importance of packaging a theory.

Gell-Mann's accomplishment -- among the most spectacular to emerge in the second half of the century -- is often compared to Dmitri Mendeleev's Periodic Table of the Elements, in which the hundred or so different atoms line up to form columns of substances with common properties: the noble gases, the rare earth metals, and so forth. The source of the order wasn't understood until scientists discovered that atoms, whose name means "indivisible," actually had minute parts. Elements that behaved in a similar manner had the same number of electrons in their outermost shells, the chemical faces they showed to the world.

Gell-Mann's crowning achievement was to see that the order of the Eightfold Way could be explained if subatomic particles also had structure. Instead of being a featureless glob of positive charge, as had been widely assumed, a proton was made of three tiny particles called quarks. Neutrally charged neutrons were made of a different combination. (Again Gell-Mann wasn't the only one to come to this realization. A young physicist named George Zweig devised a practically identical theory almost simultaneously, calling the units "aces.")
Feynman didn't find the idea particularly appealing. He all but ignored quarks until the late 1960s, when experimenters, firing electron bullets at protons, struck what appeared to be hard little objects inside. His interest finally piqued, Feynman immediately went to work analyzing the experiment, infuriating Gell-Mann by refusing to call the subparticles quarks. He insisted on his own name, "partons." Gell-Mann couldn't believe Feynman's temerity. A mongrel of Latin and Greek, "parton" was to his ear extremely ugly. Gell-Mann started calling them "put-ons," and grumbled that Feynman was trying to hijack his theory.

BY the mid-1980s what had begun as a friendly rivalry was a bitter feud. Gell-Mann had become notorious for his bad temper. Among his cronies, the nasty names he coined for rivals were as familiar as the catchy terminology he applied to particles. Leon Lederman was "the plumber," because he was an experimenter rather than a theorist. The distinguished theorists C. N. Yang and T. D. Lee were "those two Chinamen from New York."

Gell-Mann respected Feynman too much to saddle him with an insulting name. But Feynman was driving him crazy. Though hardly a prude, Gell-Mann would bristle as Feynman ebulliently described his latest escapades at the Esalen Institute, the New Age spa at Big Sur. Feynman would mock the fuzzy-headed philosophy of the place as he soaked in a hot tub and flirted with naked sunbathers.

The breaking point came in 1985, when Feynman and Ralph Leighton, the son of a Caltech physicist, compiled some of Feynman's tales into "Surely You're Joking, Mr. Feynman!": Adventures of a Curious Character, which became a surprise best seller. In story after story Feynman came off as the holy fool seeing through everyone else's pretenses. Flipping through the pages, Gell-Mann found Feynman's account of the theory of the weak nuclear force, the one they had reluctantly collaborated on. "I was very excited," Feynman said. "It was the first time, and the only time, in my career that I knew a law of nature that nobody else knew." Gell-Mann, enraged, said he would sue. In a later edition Feynman conceded that Gell-Mann and two other physicists had also thought of the idea. But the disclaimer didn't heal the wound.

For all his accomplishments, Gell-Mann couldn't be happy until he had written a best seller like Feynman's. Adding to his melancholy, "Surely, You're Joking" was followed in 1988 by Stephen Hawking's A Brief History of Time, which sold more than nine million copies. To Gell-Mann's colleagues, a book of light-hearted anecdotes told by their intense and pedantic friend seemed a dubious prospect. It would have to be called, one of them said, "Dammit, Murray, You're Right Again!" Others remarked that Gell-Mann, unlike Hawking, didn't have the advantage of being confined to a wheelchair.

"I'm writing a book for peasants," Gell-Mann would say dismissively. As it turned out, he wasn't up to the task. The Quark and the Jaguar became legendary in publishing circles for the size of the advances it attracted -- reported to be more than a million dollars worldwide -- and for the toll in human suffering it took on friends, colleagues, ghostwriters, editors, and, finally, readers. It was the Heaven's Gate of science books.

Submitted late and incomplete, the manuscript, composed one agonizing sentence at a time, was rejected by Bantam Books. Shortly afterward Gell-Mann had a mild heart attack. When the book was finally resold, for substantially less money, it did well, but on a far smaller scale than Feynman's. Gell-Mann just couldn't match Feynman as a storyteller. And although Feynman didn't actually write his own books, many of his lectures, transcribed for the popular-science market, were gems of clarity and color. Feynman thought in pictures, Gell-Mann in abstractions. When Gell-Mann tried to convey his ideas to the public, the explanations often fell flat. Making up funny names for particles, it turned out, wasn't enough.

IN the end, Gell-Mann may turn out to be the more important physicist. The Eightfold Way and quarks now lie at the foundation of the Standard Model -- the theory that explains how matter is made. It is hard to imagine a more far-reaching contribution to understanding the physical world. Trying to pin down Feynman's significance is much harder. He himself considered his Nobel Prize-winning work more of a virtuoso technical performance than a meaningful insight into nature, and it was completed when he was thirty. After that he made scattered contributions -- a theory of a phenomenon called superfluidity, for example. His greatest legacy may be Feynman diagrams, the little pictures that vividly describe particle interactions. (Gell-Mann would deny him even that distinction, obstinately calling them "Stückelberg diagrams," after an obscure Swiss physicist who devised a similar notion.)

Neither Feynman nor Gell-Mann got what he most wanted. Feynman never stopped lamenting that he had missed the thrill of being the first to understand a new truth. Gell-Mann has never become a household name. And the friction between them prevented the kind of alliance that might have led to even greater discoveries -- great enough, perhaps, to satisfy both these impossible men.

(The online version of this article appears in two parts. Click here to go to part one.)